Added flag has_primary_key_set to Model

Now we know whether the primary key is defined or not
and we do not allow to make update/remove if the key is not defined.

And when doing insert/update we can put NULL if child models don't have
the primary key set (fields with has_foreign_key set to true).

Now in after_select() we should also set has_primary_key_set flag
or just call get_last_sequence_for_primary_key instead of get_last_sequence.

fixed: added prefix +00 when serializing PT::Date to PostgreSQL (time zone)
(for a column with a time zone there was a wrong value saved)

samples/Makefile

@@ -7,13 +7,13 @@ GLOBAL_WORKING_DIR := $(shell pwd)/../..
 endif
 
 
-CXX          = g++7
+CXX          = g++10
 #CXX          = clang++
 
 # -fsanitize=address
 # -Wl,-rpath=/usr/local/lib/gcc5 or just compile with -static-libstdc++
 
-CXXFLAGS     = -Wl,-rpath=/usr/local/lib/gcc7 -Wfatal-errors -fPIC -Wall -pedantic -O0 -g3 -gdwarf-2 -pthread -std=c++17 -I/usr/local/include -I$(GLOBAL_WORKING_DIR)/pikotools -I$(GLOBAL_WORKING_DIR)/morm/src
+CXXFLAGS     = -Wl,-rpath=/usr/local/lib/gcc10 -Wfatal-errors -fPIC -Wall -pedantic -O0 -g3 -gdwarf-2 -pthread -std=c++20 -I/usr/local/include -I$(GLOBAL_WORKING_DIR)/pikotools -I$(GLOBAL_WORKING_DIR)/morm/src
 LDFLAGS      = -L/usr/local/lib